As shown in FIG. 1, a prior art paint brush comprises two handle pieces 1 and 2, a fitting seat 3, and an application head 4. The two handle pieces 1 and 2 are provided at the fastening end thereof with a slot 1a, 2a, whereas the fitting seat 3 is provided with two guide rails 3a opposite to each other. The two handle pieces 1 and 2 are fastened with the fitting seat 3 such that the guide rails 3a are respectively retained in the slots 1a and 2a of the two handle pieces 1 and 2 in conjunction with a plurality of pins 5, The application head 4 can be replaced only after the fastening pins 5 are removed from the handle pieces and the fitting seat.
As shown in FIG. 2, another prior art paint brush comprises a handle 6 and an application head 7. The handle 6 is provided at the fastening end thereof with a plurality of retaining holes 6a, whereas the application head 7 is provided at the fastening end thereof with a plurality of retaining pins 7a corresponding in location and number to the retaining holes 6a. The application head 7 is detachably fastened with the handle 6 such that the retaining pins 7a are retained in the retaining holes 6a. This prior art paint brush is defective in design in that the handle 6 and the application head 7 can not be held together securely by retaining holes 6a and the retaining pins 7a, which are susceptible to wear resulting from the friction. In addition, both hands of a user of the paint brush are easily tainted with the paint in the midst of replacing the application head 7.